In the co-pending applications of Cuneo et al., No. 07/532,329, filed Jun. 5, 1990, Goldbach et al., No. 07/678,802, filed Apr. 1, 1991, and Goldbach et al., No. 07/713,990, filed Jun. 12, 1991, there are disclosed apparatus and methods for constructing a novel double-hulled product, which as panels, modules and midbodies, are useful in the construction of vessels, in particular, bulk carriers for crude oil and other products.
The present invention relates to improvements in the method and products disclosed in the above-identified, earlier applications, the contents of which are incorporated herein by reference.
In general, the invention relates to providing a double-hulled vessel which, compared with conventional constructions, is made with a reduced number of different pieces, a reduced complexity, which can be fabricated using a higher degree of automation, which, in many applications is more durable and/or needs less maintenance, and need not cost the 20 percent additional that a conventional double hull costs compared with a conventional single hull. In fact, in some instances, a double hull produced in accordance with the invention can successfully compete in price with a conventional single hull for the same duty and carrying capacity.
Compared with the apparatus, methods and products disclosed in the above-mentioned, earlier patent application of Cuneo et al., the above-mentioned earlier applications of Goldbach et al., teaches a modified method for constructing and coating the painted subassemblies, for assembling the painted subassemblies into modules of the hull,, for launching the modules into the water on their sides, for outfitting the modules while in the water by installing fabricated piping and auxiliary structure through the open end of each module, for retrieving each outfitted module from the water while simultaneously turning each module into its final upright position and for joining each module to a respective adjacent module.
As a result of a 1970's convention entered into by the major maritime shipping nations (the "MARPOL Convention"), bulk petroleum carrier ships must have separate tanks for ballast and cargo oil. Ships thereupon necessarily became larger in overall size for carrying the same amount of cargo. Fewer bulk petroleum carrier ships were built to this requirement than had been built to serve the same market within a comparable prior period. Also, new and aggressively expanding factors in the bulk cargo vessel field sought to capture market share by cutting out what they deemed excess weight in the construction of hulls for such vessels. Part of the reduction was accomplished by using high tensile strength steel, but some was accomplished by reducing the safety margin in the thickness, spacing and redundancy of constructional elements conventionally provided to accommodate loss of strength due to corrosion occurring during the expected life of the vessel. At the same time, carrying only ballast in certain tanks of the vessel, due to requirements of the MARPOL Convention, caused accelerated corrosion. The need for better coatings was not recognized soon enough; therefore, it is now believed that many bulk cargo-carrying ships built within the last 15 years will have unpredictably short useful lives.
A conventional double-hull tanker lets ballast be carried between hulls. Such a ship does not need to be any larger, overall, than a conventional single-hull, segregated-ballast tanker.
It is believed that in the period from 1990 to 2010, the number of tankers requiring replacement or remidbodying, assuming modest expansion of world fleet requirements, an average vessel life of 25 years, and an average vessel size of 85,000 DWT, is about 180 to 200 tankers per year.